Surface Chemical Modification Of SiC And Its Effect On The Green Body After Molding

Silicon carbide(SiC)has many advantages such as high temperature strength,thermal shock resistance,high hardness and corrosion resistance.It is widely used in aerospace,electronics,automotive,biotechnology,energy,machinery,chemical and other fields.The key to obtain high-density SiC products is to prepare high solids content,low viscosity and stable dispersion of SiC slurry.In this paper,micron SiC powder was used as raw material,and SiC raw powder was modified by adding different surfactants,Then,the modified SiC powder was mixed with SiC coarse powder with d50=100 ?m and deionized water,SiC slurry was prepared by mechanically stirred,SiC green body obtained by slip casting.Addition amounts of all the modifiers and modification conditions were studied,density and microstructure of the green body after molding were studied,and the modification mechanism was further discussed.The results showed that when the silane coupling agents KH560,polyethylene glycol 400(PEG400)and tetramethylammonium hydroxide(TMAH)are used as surfactants.The addition amounts of KH560,PEG400 and TMAH were 0.5 wt%,0.8 wt%and 0.75 wt%,respectively.the reaction temperature was 90?,the reaction time was 3 h.the slurry prepared from the modified powder had the lowest viscosity and the slurry was stable The molecular weight of PEG had a certain influence on the viscosity of the slurry prepared from the modified SiC powder.When the molecular weight of PEG is 400,the viscosity of the slurry was the lowest.The pH of the modified SiC powder was around 9.When the solid content of SiC aqueous suspension was 50 vol%,the lowest viscosity was 0.305 Pa-s;At the pH value of 10,the absolute value of zeta potential was 54.3 mV,which was increased by 7.0 mV;The highest density of the green body was 2.538 g/cm3,a certain amount of small pores exist inside the green body,and a certain degree of spallation occurs.When the KH560,sodium humate and sodium dodecyl sulfate(SDS)were used as surfactants,the addition amounts of KH560,sodium humate and SDS were 0.5 wt%,0.7 wt%and 0.1 wt%,respectively.When the reaction temperature was 90? and the reaction time was 2 h,the slurry prepared from the modified powder had the lowest viscosity and the slurry was stable.The pH of the modified SiC powder was around 8.In this modification scheme,due to the addition of SDS,a certain amount of bubbles existed in the slurry prepared from the modified SiC powder,and the F-801 defoaming agent was found to be effect during the experiment,which was better than NXZ defoamer and DF-254 defoamer.When the solid content of SiC aqueous suspension was 50 vol%,the lowest viscosity was 0.168 Pa s;At the pH value of 10,the absolute value of zeta potential was 61.6 mV,which was increased by 14.3 mV;the highest density of the green body was 2.643 g/cm3.The green body has low porosity.When hexamethylene diisocyanate(HDI),tannic acid and tyrosine(Tyr)were used as surfactants,the addition amounts of HDI,tannic acid and Tyr were 0.3 wt%,0.6 wt%,and 0.6 wt%,respectively.When the reaction temperature was 800 C and the reaction time was 1.5 h,the slurry prepared from the modified powder had the lowest viscosity and the slurry was stable.The pH of the modified SiC powder was about 5.When the solid content of SiC aqueous suspension was 50 vol%,the lowest viscosity was 0.893 Pa·s;At the pH value of 10,the absolute value of zeta potential was 67.2 mV,which was increased by 19.9 mV;The highest density of the green body was 2.585 g/cm3,and a certain amount of small pores exist inside the green body.